[lldb/Plugins] Add Attach capabilities to ScriptedProcess

This patch adds process attach capabilities to the ScriptedProcess
plugin. This doesn't really expects a PID or process name, since the
process state is already script, however, this allows to create a
scripted process without requiring to have an executuble in the target.

In order to do so, this patch also turns the scripted process related
getters and setters from the `ProcessLaunchInfo` and
`ProcessAttachInfo` classes to a `ScriptedMetadata` instance and moves
it in the `ProcessInfo` class, so it can be accessed interchangeably.

This also adds the necessary SWIG wrappers to convert the internal
`Process{Attach,Launch}InfoSP` into a `SB{Attach,Launch}Info` to pass it
as argument the scripted process python implementation and convert it
back to the internal representation.

rdar://104577406

Differential Revision: https://reviews.llvm.org/D143104

Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>

lldb/examples/python/scripted_process/scripted_process.py

@@ -163,6 +163,18 @@ class ScriptedProcess(metaclass=ABCMeta):
         """
         return lldb.SBError()
 
+    def attach(self, attach_info):
+        """ Simulate the scripted process attach.
+
+        Args:
+            attach_info (lldb.SBAttachInfo): The information related to the
+            process we're attaching to.
+
+        Returns:
+            lldb.SBError: An `lldb.SBError` with error code 0.
+        """
+        return lldb.SBError()
+
     def resume(self):
         """ Simulate the scripted process resume.